Cathode-luminescent panel lamp, and method

ABSTRACT

A cathode-luminescent panel lamp (20) includes an evacuated tube (21) having a phosphor coating (25) on the inside surface of a face plate (24). An electron gun (28) is arranged to discharge at least one conical beam of electrons toward the coating to form an electron cloud within the tube. Shaping electrodes (29,30) positioned within the tube distribute and normalize the electron density of the cloud as a function of the angle (θ). The electrons pass through a field-separating mesh (39) to impinge upon a secondary emission mesh (40), which amplifies the electron density. The amplified electrons excite the phosphor coating to produce light of substantially-constant intensities across the face plate. The improved lamp may be used to back-light an LCD or in a stadium display.

Field of the Invention

The present invention relates generally to the field of luminescentpanels and lamps, and, more particularly, to an improved evacuated tubein which a cloud of electrons issuing from a cathode are firstdistributed and normalized to shape the cloud, and are then directed,with magnification of the electron density, against a phosphor coatingon the inside surface of a face plate to produce a uniform illuminationof the entire area of the face plate.

BACKGROUND ART

In recent years, there has been an increasing tendency to use liquidcrystal displays (LCD's), dot matrix displays, and other flat displaysin modern avionics. Such devices typically offer the advantages of longlife, lower power consumption, high resolution and definition, andmulti-colored displays.

At the same time, it is necessary to back-light the display in orderthat its indicia and information may be seen against a contrastingbackground. To date, several back-lighting techniques have beendeveloped. These techniques include the use of fluorescent illumination,electro-luminescent panels, incandescent lighting and gangedlight-emitting diodes (LED's). Each of these prior art techniques isbelieved to have individual disadvantages and shortcomings.

For example, fluorescent lamps must be operated continuously in order toback-light the display. This causes considerable heat to be generated.Fluorescent lamps are also temperature-dependent, particularly duringstart-up conditions. The light output of such lamps may vary by a factorof about 100 within an operating range of from about -20° C. to about+40° C. During cold start-up conditions, considerable heat is requiredto initially vaporize the mercury, and to break down the vapor into aself-maintaining discharge. This discharge, which is rich in ultravioletradiation, excites a visible radiation from a phosphor or fluorescentcoating on the inside of the tube. The particular wavelength of lightgenerated by mercury vapor (i.e., λ_(Hg) =254 nanometers) is believed todestabilize the silicon transistor matrix in the LCD. Another problem isthat fluorescent lamps are usually formed as elongated tubes. Hence, itis necessary to diffuse the light from such tubes to uniformlyilluminate a large area behind the LCD display. While the efficiency ofthe phosphor used in fluorescent lamps is typically on the order ofabout 80 lumens per watt, such tubes normally have a maximum output ofabout 6,000 foot-Lamberts (ft-L). In passing through the diffuser andthe LCD display itself, however, the intensity of light available forusable display contrast may be dramatically reduced to about 200 (ft-L).While this level may be acceptable under normal room conditions, underconditions of brilliant sunshine, such as in the cockpit of an aircraft,the ambient light intensity may be on the order of about 10,000 ft-L,thereby making the display difficult to read. In effect, a high level ofambient light may literally "wash out" the normal contrast between thedisplayed information and the background illumination. Additionaldetails of such fluorescent back-lighting techniques may be found inMercer and Schoke, "Fluorescent Backlights for LCDs", InformationDisplay at pp. 8-13 (Nov. 1989), and Kishimoto and Terada, "FlatFluorescent Lamp for LCD Back-Lighting", SPIE, Vol. 1117, DisplaySystems Optics II at pp. 168-176 (1989 ).

It is also known to use electro-luminescent panels to back-light an LCDdisplay. With such panels, the problem of non-uniformity is minimal.However, two other problems become evident. Such panels are considerablyless bright than fluorescent tubes. Luminances on the order of about 30ft-L are commonly reported. Secondly, these panels are alsotemperature-dependent, and it is necessary to heat the panel in order tomaintain even limited brightness. As much as 17 watts per square inch[2.635 watts/cm² ] of power may be required during cold starts.Moreover, the amount of light generated decreases over time. With somepanels, light output is expected to decrease by about fifty percentafter about 1500 hours of use. Additional details of suchelectro-luminescent panels may be found in U.S. Pat. No. 4,767,965("Flat Luminescent Lamp for Liquid Crystalline Display"), and U.S. Pat.No. 4,143,404 ("Laminated Filter-Electro-luminescent Rectifier Index forCathode Ray Display").

Incandescent lamps have also been used to back-light an LCD display.However, non-uniformity of illumination is a common problem. Moreover,these lamps are relatively inefficient, as compared with fluorescenttubes, and usable life is somewhat limited. As a result, incandescentlamps are not believed to be in common use for back-lighting LCD's.

Finally, ganged LED's have also been used as back-light sources. Hereagain, uniformity of illumination is a persistent problem, typicallyrequiring the use of a diffuser. Moreover, power consumption istypically greater than with fluorescent tubes and electro-luminescentpanels.

Accordingly, there is believed to be a need for an improved means forback-lighting an LCD or dot matrix display, which affords the advantageof high-contrast with the LCD under extreme conditions of ambientlighting, which has a controllable brightness, which is reliable, whichaffords uniform illumination of the display, which has a long servicelife, and which does not require heating.

DISCLOSURE OF THE INVENTION

With parenthetical reference to the first disclosed embodiment for thepurpose of illustration, this invention provides, in one aspect, animproved cathode-luminescent panel lamp (e.g., 20) which broadlyincludes: an evacuated tube (e.g., 21) having a face plate (e.g., 24)and having a phosphor coating (e.g., 25) provided on the inside surfaceof the face plate, the phosphor coating functioning as an anode andbeing operatively arranged to convert electrons impinging thereon intolight passing through the face plate; an electron gun (e.g., 28)arranged within the tube in spaced relation to the phosphor coating, thegun being operatively arranged to selectively emit at least one beam ofelectrons toward the coating to form an electron cloud within the tube;and shaping means (e.g., 29,30) operatively arranged within the tubebetween the gun and coating for causing the intensity of light emittedby the coating through the face plate to be substantially uniform acrossthe area of the coating.

The shaping means may be in the form of shaping electrodes (e.g., 29,30)provided within the tube and provided with a suitable voltage, todistribute and normalize the density of the electron cloud with respectto the phosphor coating so that the density of the electron cloudimpinging upon the phosphor coating will be substantially constant; asecondary emission coating (e.g., 84) provided on the inside surface ofthe tube for generating a secondary emission of electrons (again withthe object of distributing and normalizing the electron cloud withrespect to the phosphor coating); and a variable-efficiency orvariable-density emission coating provided on the secondary meshpositioned between the electron gun and the phosphor coating (again withthe object of distributing and normalizing the electron cloud withrespect to the phosphor coating), or in some other form.

In another aspect, the invention provides an improved method of creatinga substantially-uniform illumination of an area, with accompanyingcontrol over the brightness of such area, which method comprises thesteps of: providing an evacuated tube (e.g., 21) having a face plate(e.g., 24) through which light is to pass; providing a phosphor coating(e.g., 25) on the inside surface of the face plate; providing anelectron gun (e.g., 28) within said tube in spaced relation to thecoating; causing the gun to emit at least one beam of electrons towardthe coating to form an electron cloud within the tube; and shaping theelectron cloud such that an electron cloud of substantially-uniformdensity as a function of the angle (i.e., θ) or radial distance from thecenter of the face plate, will impinge on the entire area of thephosphor coating; thereby to excite the phosphor coating to emit lightthrough the face plate of substantially-uniform intensity over itsentire area.

Accordingly, the general object of the invention is to provide animproved cathode-luminescent panel lamp, which is particularly usefulfor, but not limited to, back-lighting an LCD display.

Another object is to provide an improved panel lamp which requires noadditional reflectors of diffusers in order to obtainsubstantially-uniform light intensity over the illuminated area.

Another object is to provide an improved panel lamp, which isparticularly useful in back-lighting an LCD display and in which theintensity of the light generated is uniform and may be varied.

Another object is to provide an improved means for back-lighting an LCDwhich does not produce light in the ultraviolet range, which mightotherwise adversely affect various parts and components of the LCD.

Another object is to provide an improved means using an electron gun toproduce a cloud of electrons which is used to produce light ofsubstantially-constant intensity over the entire illuminated area foruniformly back-lighting an LCD display.

Another object is to provide an improved means for back-lighting an LCDwhich offers the advantage of reduced power consumption, increasedreliability, controllable and selectively increased brightness, thecapability of displaying various graphic images in addition toalpha-numerics, which offers increased efficiency, and in which theintensity of back-lighting is selectively adjustable to adjust forchanges in ambient lighting conditions.

Still another object is to provide an improved panel lamp which isparticularly suited for use in a matrix or rectangular array, such as ina stadium scoreboard or display.

These and other objects and advantages will become apparent from theforegoing and ongoing written specification, the drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic fragmentary vertical sectional view of a firstform of the improved lamp, showing the space charge effect electron gun,the field-separating mesh, the secondary emission mesh, the phosphorcoating on the inside surface of the face plate, and further showing anLCD arranged immediately in front of the face plate to be back-lightedby the improved lamp.

FIG. 2 is a front elevation of the LCD shown in FIG. 1, illustratingexemplary information on the LCD as being back-lighted by the improvedlamp.

FIG. 3 is an enlarged schematic fragmentary vertical sectional view ofthe space charge effect electron gun shown in FIG. 1.

FIG. 4 is a schematic fragmentary vertical sectional view of a secondform of the improved lamp, showing an elemental electron gun, thefield-separating and secondary meshes, the phosphor coating on theinside surface of the face plate, and the LCD display arrangedimmediately in front of the face plate.

FIG. 5 is a schematic fragmentary vertical sectional view of theelemental electron gun shown in FIG. 4.

FIG. 6 is an illustrative plot of electron density (ordinate) vs. radialdistance from x--x axis (abscissa), showing that the density of theelectron cloud approaching the secondary emission mesh is substantiallyconstant and falls within a particular bandwidth.

FIG. 7 is a schematic fragmentary vertical sectional view of a thirdform of the improved lamp, showing the elemental electron gun as beingarranged to discharge conical beams of electrons at various angles withrespect to the cathode to form an electron cloud, and further showingsome of the electrons having the greatest angle θ as impinging upon asecondary emission coating on the inside surface of the tubeintermediate funnel portion.

FIG. 8 is a front elevation of the secondary emission mesh shown in FIG.7, this view graphically depicting the that the density of the secondaryemission coating thereon increases as a function of the radius R fromcenterline axis x--x.

FIG. 9 is a plot showing radial distance R from axis x--x (ordinate) vs.electron cloud density (abscissa) of the embodiment shown in FIGS. 7 and8 both immediately before and immediately after the secondary emissiongrid.

FIG. 10 is a schematic front elevation of a fourth form of the improvedlamp, showing four individual lamps as being arranged in a rectangulararray or matrix.

FIG. 11 is a fragmentary schematic vertical sectional view of the fourthform shown in FIG. 10, showing the adjacent lamps as sharing commonintermediate wall portions, with the field-separating and secondaryemission grids spanning all four lamps.

MODE(S) OF CARRYING OUT THE INVENTION

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., arrangement of parts, mounting, etc.) together withthe specification, and are to be considered a portion of the entirewritten description of this invention. As used in the followingdescription, the terms "horizontal", "vertical", "left", "right", "up"and "down", as well as adjectival and adverbial derivatives thereof(e.g., "horizontally", "right-wardly", "upwardly", etc.) simply refer tothe orientation of the illustrated structure as the particular drawingfigure faces the reader. Unless otherwise indicated, the terms"inwardly" and "outwardly" refer to the orientation of a surfacerelative to its axis of elongation, or axis or rotation, as appropriate.

Turning now to the drawings, the present invention provides an improvedcathode-luminescent lamp which is particularly adapted for use inback-lighting LCD's, dot matrix displays, and the like. However, theinvention is deemed to have utility apart from this particularback-lighting use, as described infra. Hence, the invention should notbe limited to this particular environment or use, unless an explicitlimitation to that effect appears in the appended claims. Several formsof the improved lamp are disclosed herein. A first form is shown inFIGS. 1-3, a second in FIGS. 4-6, a third in FIGS. 7-9, and a fourth inFIGS. 10-11. These four forms, as well as various modifications thereof,will be discussed seriatim herebelow.

First Form (FIGS. 1-3)

Referring now to FIGS. 1-3, a first form of the improved lamp, generallyindicated at 20 in FIG. 1, is shown as including an evacuated tube 21having a leftward neck portion 22, an intermediate rightwardly-divergentfunnel portion 23, and a rightward planar vertical face plate 24provided with a suitable phosphor coating 25 on its inside surface. Tube21 is shown as being elongated along horizontal axis x--x and has anaxial length L and a face plate diameter (or diagonal) D. An LCD,generally indicated at 26, is positioned immediately to the right of theface place such that light produced by lamp 20 is arranged to back-lightinformation, shown to be numbers "1983" and "20" for purposes ofillustration, displayed on the LCD (FIG. 2).

Lamp 20 includes a space charge effect electron gun, generally indicatedat 28. A plurality of shaping electrodes, two of which are indicated at29 and 30, are arranged on the inside surface of funnel portion 23.Suitable voltages are provided to electrodes 29,30 via appropriate lampinput terminals, severally indicated at 31, to cause a beam of electronsto issue from the planar circular vertical emitting surface 32 of athermionic cathode 33 within the gun (FIG. 3). After leaving theemitting surface, these electrons sequentially pass through alignedapertures 34,35 of a pair of axially-spaced grids 36,38 respectively.Grids 36,38 are provided with suitable voltages via appropriate circuitinput terminals 31. The electrons (i.e., e) issuing from emittingsurface 32 are caused to first converge as they pass through the firstgrid opening 34, and then cross-over as they pass through the secondgrid opening 35 to form a rightwardly-divergent conical beam. Eachdivergent electron path has an angle θ with respect to axis x--x.Suitable voltages are provided to shaping grids 29,30 via appropriatecircuit input terminals 31. The effect of these shaping voltages is to"bend" or normalize the paths of the various non-axial electrons, as afunction of their respective angles θ, such that substantially all ofthe electrons will thereafter travel along paths substantially parallelto tube axis x--x, as schematically indicated in FIG. 1. Moreover, afterbeing so shaped and directed, the density of the electrons will besubstantially constant in a plane transverse to axis x--x.

A circular vertical field-separating mesh 39 and a circular verticalsecondary emission mesh 40 are operatively arranged in the path of thenormalized and distributed electron cloud. The field-separating meshseparates the relatively low-strength electrical field produced byshaping electrodes 29,30 from the relatively high strength fieldproduced by coated anode 25, which is provided with a suitable voltagevia appropriate circuit input terminals 31 or other connection throughtube 21. Secondary mesh 40 is provided with a suitable coating, andproduces a magnified number of electrons for every incident electronpassing through mesh 39. In effect, secondary mesh 40 increases the gainof the electron density in the cloud, while preserving the substantiallyuniform distribution of same across the projected circular area of thephosphor coating. The electrons emitted from secondary mesh 40 impingeupon phosphor coating 25, thereby exciting it to emit light ofsubstantially-uniform intensity through face plate 24 to back-light theindicia displayed on LCD 26.

In this first form, the shaping electrodes cause the divergent electronsemitted from gun 28 to be distributed substantially uniformly as theyapproach field-separating mesh 39. The secondary emission mesh 40, whichis also supplied with power via an appropriate circuit input terminal 31or other connection through tube 21, merely amplifies the number ofelectrons directed normally (i.e., perpendicularly) at the phosphorcoating, while maintaining the substantially-uniform density of theelectron distribution across the projected area of the phosphor coating.In other words, in this first form, the density of electrons strikingthe phosphor coating is not the same as the density of the electronspassing through the field-separating mesh. However, both densities aresubstantially proportional, and are uniformly distributed across theentire projected area of the phosphor coating. Hence, the lightgenerated by the phosphor coating and passing through the face platewill be of substantially-constant intensity across the area of the faceplate to uniformly back-light the LCD.

The foregoing arrangement is not invariable. In the just-described form,the divergent stream of electrons emitted by the space effect gun isfirst shaped and distributed to produce an electron cloud ofsubstantially-constant electron density across the projected area of thephosphor coating in a plane perpendicular to axis x--x. Alternatively,the electron beam need not be so shaped. For example, if the electronsissue from the cathode emitting surface as a substantially-conical beamof variable radial density, phosphor coating 25 could be formed to havea variable efficiency inversely related to the incident electrondensity. Thus, if the electron density varies inversely to angle θ, theefficiency of the phosphor coating may be reciprocally complimentary,such that the coating efficiency will be greatest where the electrondensity is least and thinnest where the electron is density is greatest,all with the object of causing the cloud striking the phosphor coatingfor producing substantially-uniform illumination of the face plateacross its entire area. Similarly, while the face plate is shown asbeing circular in the illustrated form, this need not invariably obtain.Alternatively, the face plate could have some other arcuate or polygonalshape, as desired.

In yet another variation, the inside surface of the funnel portion 23could be coated with a suitable secondary emission coating, as describedinfra, such that electrons issuing from gun 28 at a large angle willstrike the secondary emission coating and induce an amplified electrondischarge therefrom toward coating 25.

Second Form (FIGS. 4-6)

A second form of the improved lamp is generally indicated at 41 in FIGS.4-6. This second form is shown as again including an evacuated tube 21,albeit of slightly different shape, having a leftward narrowed neckportion 22, an intermediate funnel portion 23, and a rightward faceplate 24. This tube has a larger diameter-to-length ratio (i.e., D/L)than in the first form. An LCD 26 is positioned immediately in front ofthe face plate (i.e., to the immediate right of the face plate in FIG.4) so that information displayed on the LCD will be back-lighted by thelight passing through the face plate. A phosphor coating 25 is againprovided within the tube on the surface of the face plate.

In this form, however, the space effect electron gun is replaced by anelemental electron gun, generally indicated at 42. As best shown in FIG.5, gun 42 is mounted on two horizontally-spaced rectangular verticaldielectric blocks 43,44, respectively. Left block 43 is provided with acentral through-hole 45 of relatively-small diameter, and right block 44is provided with an aligned coaxial through-hole 46 of somewhat enlargeddiameter. A heater 48, connected to appropriate circuit input terminals31 via leads 49,50, penetrates openings 45,46 so as to be operativelyarranged to heat the cathode's emitting surface.

A two-piece cathode support clip 51 includes an outer part 52 and aninner part 53. The outer part is shown as being a thin-walled tubularmember generated about axis x--x, and sequentially includes: an annularvertical left end face 54, a horizontal cylindrical portion 55 extendingrightwardly therefrom, a rightwardly- and outwardly-divergentfrusto-conical portion 56, a horizontal cylindrical portion 58continuing right-wardly therefrom to be frictionally arranged withinleft block opening 45, and an annular stop portion 59 arranged to abut amarginal portion of the right face of block 43 immediately about opening45. The inner part 53 is also shown as being a thin-walled tubularmember generated about axis x--x, and sequentially includes: an annularvertical left end face 60, a horizontal portion cylindrical portion 61extending rightwardly therefrom within outer part cylindrical portion 55and engaging portion 55, a rightwardly- and inwardly-inclinedfrusto-conical portion 62, a horizontal cylindrical portion 63, arightwardly-and outwardly-inclined frusto-conical portion 64, and ahorizontal cylindrical portion 65 continuing rightwardly therefrom andterminating in an annular vertical end face 66. The cathode is shown asfurther including a cup-shaped member 68 mounted on inner member 53.Member 68 has an annular vertical left end face 69, a horizontalcylindrical wall portion 70 extending rightwardly therefrom infrictionally-engaged overlapped relation with respect to the rightmarginal end portion of inner part surface 65, and an integrallyformedrightwardly-convex hemi-spherical emitting surface 71.

A control grid 72 surrounds the cathode. Grid 72 is shown as being adeeply-drawn cup-shaped member provided with an annular vertical flange73 about its leftward open mouth. Flange 73 is held between the facingsurfaces of blocks 43,44. Grid 72 is shown as further having anintegrally-formed horizontal cylindrical portion 74 extendingrightwardly from the inner margin of flange portion 73 in axially-spacedrelation to cathode surface 70, and as having an integrally-formedrightwardly-convex hemi-spherical portion 75 arranged in spacedconcentric relation to emitting surface 71.

An accelerator grid 76 surrounds the control grid. Grid 76 is also shownas being a cup-shaped member provided with an annular vertical flange 78about its leftward open mouth. Flange 78 is adapted to be secured to theright vertical face of right block 44 by suitable means (not shown).Grid 76 also includes an integral substantially-cylindrical portion 79extending axially rightwardly from the inner margin of flange 78 inspaced relation to control grid portion 74, and an integralrightwardly-convex hemi-spherical portion 80 arranged in spacedconcentric relation to control grid surface 75. In the illustrated form,emitting surface 71 is of radius R₁, control grid surface 75 is ofradius R₂, and accelerator grid surface 80 is of radius R₃, where R₃ >R₂>R₁ and R₂ ≈ (R₁ +R₃)/2.

A plurality of pairs of radially-aligned apertures, severally indicatedat 81,82 are provided through the control and accelerator grids,respectively, at various locations about the hemi-spherical portions ofthe cathode and the two grids. Each pair of apertures functions topermit a conical beam of electrons to be emitted normally from thecathode emitting surface. These beams overlap one another at a distancefrom the gun to produce an electron cloud. In lamp 41, the shapingelectrodes 29,30 are again provided to distribute and normalize theelectron cloud as it moves rightwardly toward the meshes. Thus, as shownin FIG. 6, the electron density immediately before reaching thefield-separating mesh has a substantially-constant density (i.e., doesnot vary in magnitude by more than about 15-20%) across the projectedarea of the phosphor coating.

Third Form (FIGS. 7-9)

Referring now to FIG. 7, a third form of the improved lamp, generallyindicated at 83, is again shown as including an evacuated tube 21provided with a leftward neck portion 22, an intermediate funnel-shapedportion 23, and a rightward vertical face plate 24. A phosphor coating25 is again provided on the inside surface of the face plate, and an LCD26 is provided adjacent the outside surface of the face plate so thatindicia thereon will be back-lighted by the improved lamp. Tube 21 isalso shown as including elemental electron gun 42, as before.

This form differs from the first and second embodiments in that asecondary emission coating 84 is provided on the inside surface offunnel portion 23, in lieu of shaping electrodes 29,30. Thus, electronsissuing from gun 42 at a large angle θ will impinge coating 84, therebyexciting it to produce electrons which are directed toward thefield-separating mesh 39 and secondary emission mesh 40.

To the extent that the electron cloud between coating 84 and mesh 40 isnot of uniform electron density, the secondary emission coating on mesh40 may be reciprocally non-uniform, as shown in FIG. 8. Thus, forexample, if the density of the electron cloud decreases with the radialdistance R from axis x--x, the efficiency or density of the secondaryemission coating on mesh 40 may reciprocally increase with such radialdistance, so that the electron cloud leaving the secondary emission meshwill be widely distributed and of substantially-constant electrondensity across the entire projected area of phosphor coating 25, asshown in FIG. 9. Alternatively, if the electron density of the cloudapproaching mesh 40 has some other non-uniform distribution pattern, thethickness or density of the secondary emission coating on mesh 40 may bevaried in some other reciprocally complimentary manner so that the cloudimpinging upon coating 25 will be of substantially-constant electrondensity, all with the object of causing coating to produce light ofsubstantially-constant intensity through the face plate to back-lightthe LCD.

Fourth Form (FIGS. 10-11)

The three forms of the improved lamp heretofore described have thecapability of uniformly illuminating the face plate, regardless ofwhether an LCD is positioned in front of it or not. The various forms ofthe invention can be used for purposes other than back-lighting an LCD.

For example, as shown in FIG. 10, four or more of the improved panellamps may be arranged in a rectangular array or matrix generallyindicated at 85. This particular arrangement is illustrative only.Persons skilled in this art will readily appreciate that the number ofcolumns and rows, as well as the face plate areas of the individuallamps, may be readily changed or modified to suit the particular enduse. In any event, as shown in FIG. 11, the enclosures forming eachindividual lamp may be configured so as to share common intermediatewalls, such as indicated at 86. However, the field-separating andsecondary emission meshes 39,40, respectively may span all of theindividual lamps in the particular array. Thus, in the embodimentillustrated in FIGS. 10-11, there are four individual lamps in thearray, and these lamps may be controlled individually and independentlyof the others in the array. These various multi-panel arrays may befurther arranged in a multi-lamp matrix, such as a stadium scoreboard(not shown) or the like,

Modifications

The present invention contemplates that many changes and modificationsmay be made. As previously noted, the face plate may be round, square,rectangular, or some other arcuate or polygonal shape. While it ispreferably flat, in order to back-light a flat screen display, the faceplate need not necessarily be so. Indeed, the face plate may be concaveor convex, as desired, with an appropriate adjustment in the shapingmeans. The phosphor coating may have a substantially-constantefficiency, or a variable efficiency related inversely to the density ofthe electrons exciting the same, again with the desired object ofproducing light of substantially-uniform intensity across the entirearea of the face plate. In the preferred embodiment, the intensity ofsuch light transmitted through the face plate will not vary by more thanabout 15-20%. Moreover, the improved lamp may have an intensity on theorder of about 10,000 ft-L at the outer surface of the face plate.

The electron gun may be either of the space charge effect-type, theelemental-type, the field effect transistor-type, or may possibly be ofsome other type. The function of the shaping electrodes and/or thesecondary emission coating on the inside of the tube funnel portion, isto normalize the direction of the electron cloud within the tube, sothat the electrons will be of substantially-constant density and willimpinge upon the phosphor coating in a substantially-perpendicularmanner. The secondary emission grid is desired, since it affords thecapability of increasing the electron density immediately before thephosphor coating. However, if this feature is not desired, the secondaryemission grid may be omitted altogether.

The invention is not limited to use in back-lighting displays. Ifdesired, a number of such improved panels could be arranged in a matrix,and operated either independently or in conjunction with one another,either with or without a crystalline display superimposed thereon. Forexample, a matrix of such panels could be used in a stadium scoreboardor other display, in high-definition television (HDTV), or in a myriadof other possible applications.

Therefore, the invention broadly provides an improvedcathode-luminescent panel lamp, which broadly includes an evacuated tubehaving a phosphor coating arranged on the inside of a face plate, anelectron gun arranged within the tube in spaced relation to the coating,and shaping means arranged within the tube between the gun and thecoating for normalizing the electron cloud and for causing light emittedby the coating through the face plate to be of substantially-constantintensity. The shaping means may be in the form of shaping electrodes,an emission coating, or a variable-density secondary emission coating ona mesh that is complimentary to the approaching electron cloud.

In use, the apparatus performs the improved method of creating asubstantially-uniform illumination of a panel area, which method broadlyincludes the steps of: providing an evacuated tube having a face platethrough which light is to pass; providing a phosphor coating on theinside surface of the face plate; providing an electron gun within thetube in spaced relation to the phosphor coating; causing the gun to emita diverging beam of electrons toward the coating to form an electroncloud within the tube; and selectively shaping the beam such that theelectron cloud impinging on the coating will have asubstantially-constant electron density across the entire area of thecoating; thereby to cause the coating to emit light ofsubstantially-constant intensity through the face plate.

Therefore, while several presently-preferred forms of the improvedcathode-luminescent panel lamp have been shown and described, andseveral modifications and changes thereof discussed, persons skilled inthis art will readily appreciate that various additional changes andmodifications may be made without departing from the spirit of theinvention, as defined and differentiated by the following claims.

We claim:
 1. A cathode-luminescent panel lamp, comprising:an evacuatedtube having an optical axis, having a face plate and having a phosphorcoating arranged on the inside surface of said face plate, said phosphorcoating functioning as an anode and being operatively arranged toconvert electrons impinging thereon into light passing through said faceplate; a single electron gun arranged within said tube in spacedrelation to said phosphor coating, said gun being operatively arrangedto selectively emit at least one divergent beam of electrons toward saidphosphor coating to form an electron cloud; and shaping meansoperatively arranged within said tube between said gun and phosphorcoating for controlling the density of electrons striking said phosphorcoating as a function of their angle from said optical axis and fordistributing and normalizing the electrons in said cloud with respect tosaid face place and for causing the intensity of light emitted by saidphosphor coating through said face plate to be substantially constantacross the area of said face plate.
 2. A cathode-luminescent panel lampas set forth in claim 1 wherein said tube has a neck portion and has afunnel portion arranged between said neck portion and said face plate,and wherein said electron gun is arranged in said neck portion.
 3. Acathode-luminescent panel lamp as set forth in claim 2 wherein said gunis a space charge effect electron gun.
 4. A cathode-luminescent panellamp as set forth in claim 1 wherein said shaping means includes aplurality of shaping electrodes arranged between said gun and face plateand operatively arranged to cause the cloud of electrons impinging uponsaid phosphor coating to be substantially constant over the area of saidcoating.
 5. A cathode-luminescent panel lamp as set forth in claim 4wherein said shaping electrodes are arranged on the inside surface ofsaid tube.
 6. A cathode-luminescent panel lamp as set forth in claim 5and further comprising a field-separating mesh positioned between saidshaping electrodes and said phosphor coating for separating thepotential of said shaping electrodes from the potential of said anode.7. A cathode-luminescent panel lamp as set forth in claim 6 wherein thecloud of electrons at said field-separating mesh is distributedsubstantially uniformly across the area of said mesh.
 8. Acathode-luminescent panel lamp as set forth in claim 7 and furthercomprising a secondary emission mesh operatively arranged between saidfield-separating mesh and said coating for increasing the density ofelectrons in said cloud.
 9. A cathode-luminescent panel lamp as setforth in claim 8 wherein said secondary emission mesh increases theelectron density of said cloud.
 10. A cathode-luminescent panel lamp asset forth in claim 9 wherein said coating has a substantially-constantefficiency.
 11. A cathode-luminescent panel lamp as set forth in claim 1wherein the density of electrons impinging upon said coating is notuniform across the area of said coating, and said coating has a variableefficiency such that the light emitted by said coating and passingthrough said face plate is substantially constant.
 12. Acathode-luminescent panel lamp as set forth in claim 2 wherein said gunis an elemental electron gun.
 13. A cathode-luminescent panel lamp asset forth in claim 12 wherein said gun has a cathode provided with aconvex emitting surface and at least two grids aligned in spacedrelation to said emitting surface, and wherein said grids are providedwith a plurality of aligned apertures such that electrons will issuefrom said emitting surface through said cooperative aligned apertures asa conical electron beam.
 14. A cathode-luminescent panel lamp as setforth in claim 8 wherein said secondary mesh is provided with anemission coating, and wherein the density of said secondary emissionmesh coating is not uniform across the face of said mesh.
 15. Acathode-luminescent panel lamp as set forth in claim 14 wherein thedensity of said secondary emission mesh coating varies inversely withthe election density of the cloud approaching said secondary mesh sothat the cloud impinging said phosphor coating will have asubstantially-constant electron density across the area of said phosphorcoating.
 16. A cathode-luminescent panel lamp as set forth in claim 1wherein a plurality of said tubes are arranged in an array to form amatrix.
 17. A cathode-luminescent panel lamp as set forth in claim 16wherein said tubes share common walls.
 18. The method of creating asubstantially-uniform illumination of an area, comprising the stepsof:providing an evacuated tube having and optical axis and having a faceplate through which light is to pass; providing a phosphor coating onthe inside surface of said face plate; providing an electron gun withinsaid tube in spaced relation to said coating; causing said gun to emitat least one diverging beam of electrons toward said coating to form anelectron cloud; and shaping said electron cloud by controlling thedensity of electrons striking said phosphor coating as a function oftheir angle from the optical axis such that the electrons impinging uponsaid coating will have a substantially-uniform density across the areaof said phosphor coating; thereby to cause said phosphor coating to emitlight of substantially-constant intensity through said face plate. 19.The method set forth in claim 18 and further comprising the additionalstep of: magnifying the density of the electron cloud emitted by saidgun.